Adjustable time delay electromagnetic clutch

ABSTRACT

An electromagnetic clutch or brake including means for retarding or slowing the engagement and/or release of the armature is shown herein. An additional coil comprising one or more turns of high current capacity wire is included within the magnet body forming an electromagnetic coupling with the main coil in order to impede the generation and/or collapse of the main coil-induced electromagnetic field. A variable resistor or equivalent means is connected in series circuit relationship with the additional coil in order to selectively vary the amount of eddy current permitted to be induced in the additional coil, therefore providing means for regulating the response time of the armature to energization and deenergization of the primary coil. Control means connected in series circuit relationship with the additional coil and variable resistor comprising at least one diode and a switch may also be included so that application of the magnetically retarding coil can be selective and/or unidirectional.

United States Patent Spencer [54] ADJUSTABLE TIME DELAY ELECTROMAGNETICCLUTCH lnventor:

Assignee:

Filed:

Appl. No.:

Glenn S. Spencer, l-lorseheads, N.Y.

The Bendix Corporation Sept. 21, 1971 US. Cl. ..192/52, 192/84 R, 192/84A,

Int. Cl ..Fl6d 27/06 Field of Search ..l92/52, 84 R, 84 A, 84 AB;

References Cited UNITED STATES PATENTS Knowlton Reist PrimaryExaminerAllan D. Hermann Attorney-Bruce A. Yungman [451 Dec. 5, 1972 57] ABSTRACT An electromagnetic clutch or brake including means forretarding or slowing the engagement and/or release of the armature isshown herein. An additional coil comprising one or more turns of highcurrent capacity wire is included within the magnet body forming anelectromagnetic coupling with the main coil in order to impede thegeneration and/or collapse of the main coil-induced electromagneticfield. A variable resistor or equivalent means is connected in seriescircuit relationship with the additional coil in order to selectivelyvary the amount of eddy current permitted to be induced in theadditional coil, therefore providing means for regulating the responsetime of the armature to energization and deenergization of the primarycoil. Control means connected in series circuit relationship with theadditional coil and variable resistor comprising at least one diode anda switch may also be included so that application of the magneticallyretarding coil can be selective and/or unidirectional.

9 Claims, 2 Drawing Figures ADJUSTABLE TIME DELAY ELECTROMAGNETIC CLUTCHCROSS REFERENCE TO RELATED APPLICATIONS This case is related to mycommonly assigned copending patent applications Ser. Nos. 182,337 and182,338 filed on even date.

FIELD OF THE INVENTION This invention relates generally to a d.c. timedelay electromagnetic relay, and more particularly to an electromagneticcoupling operatively associated with an electromagnetic clutch.

BRIEF DESCRIPTION OF THE PRIOR ART When an electromagnetic clutch isenergized, the change in magnetic flux level, from zero to nominaloperating level, causes a voltage to be induced in any nearby metal. Inthe iron of the clutch magnet body and armature plate, this results in alarge eddy current which follows a circular path, opposite and parallelto the coil current and perpendicular to the flux. The magnetomotiveforce created by this eddy current opposes that of the main coil currentand results in slowing the rate at which the magnetism rises. When theclutch is deenergized, the falling flux again generates a large eddycurrent, this time flowing in the opposite direction, (i.e., in the samedirection as the coil current) producing a magnetomotive force whichaids the main field and delays its collapse. The slow magnetic responsethat such induced currents cause, both at energization and atdeenergization of the coil, is generally undesirable. Commonly assignedU. S. Pat. No. 3,327,822 covers a clutch in which an interruption in theiron ring of the magnet body and armature eliminates the eddy currentand speeds the magnetic response.

Rapid response, however, is not always a desirable feature. In singlesurface clutches of the dry friction type, for example, a slowapplication of torque is generally preferable because of the softclutching and feathering in" resulting therefrom. This is particularlytrue where a clutch has been sized to the stall torque of the primemover. Such a clutch would other deliver excessive shock torques innormal day to day service, causing abnormal wear of the clutch faces andpossible breakage of associated drive members.

SUMMARY OF THE INVENTION In order to overcome the inherent defects of arapidly responding electromagnetic clutch as described above, a secondcoil consisting of at least one complete turn of copper or other highcurrent capacity material is nested with the main coil in a cavity inthe clutch magnet body. This second coil provides a current path withmuch higher conductivity than the iron of the magnet body and results inan increased and more effective eddy current. Variable resistance meansis connected in series circuit relationship with the second coil so thatthe amount of eddy current flow through the second coil may beregulated. The generated flux of the main magnetic field having toovercome the increased magnetomotive opposition generated by the secondcoil will build and decay more slowly and clutch torque will be appliedand released more gradually, the time of flux build-up and decay being adirect function of the setting of the variable resistance means.Switching means and/or diode means connected in series circuitrelationship with the second coil and the'variable resistance means mayalso be included so that application of the magnetically retarding coilcan be selective and/or unidirectional.

It is, therefore, a primary object of this invention to provide animproved electromagnetic friction device having adjustable means forretarding the magnetic response of the electromagnetic members uponenergization and/or deenergization of the primary electromagnetic coil,so that transmitted torque will be applied and/or released moregradually.

It is another object of this invention to provide an adjustable timedelay electromagnetic clutch or brake in which the time of engagementand/or disengagement may be regulated.

It is still another object of this invention to provide an adjustabletime delay electromagnetic clutch having second electromagnetic coilmeans and variable resistance means for regulating the electromagneticresponse of the armature upon energization and/or deenergization of theprimary electromagnetic coil, the second coil means being inelectromagnetic flux circuit relationship with the primaryelectromagnetic coil.

It is a still further object of this invention to provide an adjustabletime delay electromagnetic clutch which takes advantage of the inherentcharacteristics of an electromagnetic coupling thereby retarding clutchengagement and/or disengagement by impeding the generation and/orcollapse of the coil induced electromagnetic field whenever the primarycoil is energized and/or deenergized.

It is yet another object of this invention to provide an electromagneticclutch or brake having means for slowing the electromagnetic response ofthe armature such that the torque transmission between input and outputmembers is gradually applied and/or released.

It is still another object of this invention to provide an adjustabletime delay electromagnetic clutch which eliminates-excessive shocktorques thereby prolonging the life of the clutch faces and theassociated drive members.

It is a still further object of this invention to provide in a timedelay electromagnetic clutch having second electromagnetic coil meansfor retarding the magnetic response of the armature to the primary coil,control means for selecting the desired direction of eddy current flowin the second coil means so that the second coil means will beconductive and therefore retard the response of the armature upon clutchengagement and/or upon clutch disengagement as desired.

It is a still further object of this invention to provide in a timedelay electromagnetic clutch having second electromagnetic coil meansand adjusting means for regulating the magnetic response of the armatureto the primary coil, switching means located externally of the clutch sothat the regulated retarding effect of the time delay coil may beselectively applied or completely disconnected from the electromagneticcircuit.

It is even a further object of this invention to provide in anadjustable time delay electromagnetic clutch having secondelectromagnetic coil means and regulating means for selectively varyingthe amount of eddy current permitted to flow in the second coil means,means for establishing substantially unidirectional eddy current flowtherein so that the second coil means will generate magnetomotiveopposition to a change in flux level developed by the primary coil onlywhen the second coil means is conductive, thereby retarding the magneticresponse of the armature in one direction only. The means forestablishing substantially unidirectional eddy current flow in thesecond coil means is located externally of the clutch so that thepermitted direction of eddy current flow may be selected or changedexternally, either by manual or automatic control.

Other objects and advantages of this invention will become apparent fromthe following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic partialcross-sectional view of the preferred embodiment of my electromagneticclutch. I

FIG; 2 is a schematic of the coil of my invention and its accompanyingcontrol means shown in FIG. 1.

' DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1of the drawing, my electromagnetic clutch is shown, generally designatedby numeral 10. The clutch includes a rotatable magnet body 12 adapted tobe secured to a first torque transmitting means, power shaft 14, bymeans of a key and key-way slot shown generally as 16. Although thepreferred embodiment relates specifically to an electromagnetic clutch,it should be obvious to those skilled in the art that the teaching of myinvention may be equally applied to an electromagnetic brake where themagnet body member 12 does not normally rotate; also, my invention wouldbe equally effective in a stationary field clutch where the coil 20 andmagnet body 12 are nonrotatable members. Magnet body 12 is fabricated ofmagnetic flux conducting material such as iron or steel. An annularrecess or cavity 18 is formed within the magnet-body 12 and has disposedtherein the primary electromagnetic coil 20 and the separate butsubstantially adjacent time delay coil 30 of my invention. Coils 20 and30 may be secured within cavity 18 by resin or other conventional means.

Coil 20 has two leads, 21 and 22; lead 21 is connected to ground andlead 22 is connected to slip ring 24. Slip ring 24 is fixedly secured toan annular electrical insulation member 26. Member 26 is fabricated fromrubber or other suitable electrical insulating material and is mountedon an axially extending shoulder 13 provided on magnet body 12.Electrical power is supplied to slip ring 24 from battery 40 throughlead 29 which is connected to a brush 28. Lead 29 and power source 40are in circuit relationship with a control circuit shown generally asthe box 50, which control circuit triggers the energization and/ordeenergization of the primary coil 20.

The clutch of the present invention is reversible with respect to inputand output sides and thus, clutch structure which in one installationwould be an input member in another installation would be an outputmember. Accordingly, rotating input and output members are referred togenerically as first and second torque transmitting members.

.luxtaposed and coaxially aligned with magnet body 12 is armature 60.Armature 60 is slidably splined to the terminal end of second torquetransmitting means, power shaft 62. Armature 60 is adapted to movetoward and away from engagement with the magnet body 12 uponenergization and deenergization of the electromagnetic coil 20. Theaxial mating faces of magnet body 12 and armature 60 are the clutchfaces through which torque is transmitted. Of course, my invention couldalso be used in a multiple disc clutch, a cone type clutch, etc., wherethe magnet body and the armature are not the principal torquetransmitting friction members.

Coil 30 also has two leads, 92 and 93; lead 92 is connected to groundand lead 93 is connected to slip ring 94 which is fixedly secured toannular insulation member 26 in a manner similar to slip ring 24. Theinduced current developed in coil 30 is carried to control means throughbrush 95 and lead 96.

Referring to FIG. 2, coil 30 is shown as a discontinuous double turn ofhigh current capacity wire, the terminal ends of which are mounted tolead wires 92 and 93. Coil 30 is preferably fabricated from copper orother conductive material which provides a current path with much higherconductivity than the iron of magnet body 12 thus producing a strongermore effective eddy current. It would be obvious to those skilled in theart that the actual configuration of coil 30 is a matter of designchoice, since without taking into account control means 90 describedbelow, it is the crosssectional area of coil 30 that is normallydeterminative of the armatures response time; e.g., a solid ring oftwice the cross-section will provide the same time delay effect as thetwo rings shown. Without regulating the amount of eddy current permittedto develop in coil 30, the cross-sectional area of coil 30 and thearmature response time are directly proportional, holding the size andstrength of coil 20 constant; that is, the larger the cross-sectionalarea of coil 30, the longer the response time of the armature.

Coil 30 is shown as having substantially the same diameter of coil 20,both coils being coaxial and perpendicular to the axis of the clutch.However, it is important to recognize that the diameter and position ofcoil 39 relative to coil 29 is unimportant so long as an electromagneticcoupling is formed by the two coils and the coils are, therefore, inelectromagnetic flux circuit relationship. For example, time delay coil30 would still perform its function if it were disposed around the 0.1).of primary coil 20, or within its l.D., or at any other position so longas it embraced the magnetic field generated by the primary coil 20. r

The control means 90 which is in communication with coil 30 through lead96 as described above, consists of a four-position switch 91, two diodes98 and 99 which are in parallel circuit relationship with lead 96 andtwo of the terminals of the switch 9H, a lead 97 interconnecting lead 96to one terminal of switch 91, and a variable resistor 100 connected inseries to the ground terminal of switch 91. The four operative positionsof switch 91, position A, position 8, position C,

and position D are as follows: position A is the open circuit position;position B is the closed circuit position which interconnects coil 30and the variable resistance means 100; position C connects switch 91 tothe cathode of diode 98; and, position D connects switch 91 to the anodeof diode 99. Switching means 91 of control circuit means 90 may bemanually moved between the above mentioned positions, or movement ofswitch 81 may be automatically controlled as a feedback or otherfunction of a separate control circuit (not shown).

Reference has been made throughout to variable resistance means,adjusting means, regulating means, all three means being usedsynonymously. Although I have specifically shown a variable resistor 100as part of the control means 90, one skilled in the art would realizethat substantially equivalent mechanical forms of the variable resistorinclude a potentiometer and a rheostat, which two devices may also beused with equal effectiveness in my invention. The type ofelectromechanical device chosen to be used in control means 90 will bedictated by the environment in which my clutch is sued. For example,although a potentiometer and a variable resistor are basically the same,a rheostat is a variable resistor which has one fixed terminal and amovable contact. Potentiometers may be used as rheostats, but a rheostatcannot be used as a potentiometer because connections cannot be made toboth ends of the resistance element. Therefore, use of the three more orless generic terms noted above has been made throughout since the typeof device used to vary the resistance is relatively immaterial so longas manual or automatic means for accomplishing this function is includedin the time delay circuit.

OPERATION OF THE PREFERRED EMBODIMENT Switch Position A When clutchengagement is desired, a control signal is generated from the controlcircuit 50 and power is carried to coil by means of the lead wires 22and 29 and the brush and slip ring 28 and 24 thereby energizing coil 20.The change in flux linkage generated by coil 20 from zero to nominaloperating level (the quiescent state) causes an electromotive force(emf), i.e., a voltage, to be induced across coil 30. Since coil 30provides a current path with much higher conductivity than the iron ofmagnet body 12, a larger more effective momentary or eddy current wouldnormally be induced in coil 30. However, with switch 91 in position A,an open circuit condition exists and therefore no eddy current can bedeveloped in coil 30. The response of the clutch in this position isnormal since coil 30 will not conduct a current either upon energizationor deenergization of the primary coil 20. Switch Position B When clutchengagement is desired, a control signal is generated from the controlcircuit 50, coil 20 is energized, and a voltage is induced across coil30 as described above. This emf induces a momentary or eddy current incoil 30 which follows a generally circular path opposite in directionand parallel to the primary coil current and perpendicular to the fluxlinkage generated by primary coil 20. A magnetomotive force created bythis eddy current opposes that of the main coil current and results inslowing the rate at which magnetism rises in magnet body 12. The flux ofthe main magnetic field, having to overcome this increased opposition,will build more slowly thereby retarding the movement of armature intoengagement with magnet body 12; thus, clutch torque will be applied moregradually. If the clutch response time (the time it takes armature 60 tomove into contact with magnet body 12 upon energization of primary coil20) is to be increased, the resistance in the electromagnetic circuitshown in FIG. 2 is decreased by making the proper change in setting ofthe variable resistor 100. The decreased resistance permits a higherinduced current in coil 30, resulting in a larger counter magnetomotiveforce and a corresponding reduction in the rate at which the mainmagnetic field rises. Therefore, armature 60 is drawn more slowly intocontactive engagement with the magnet body 12. If the clutch responsetime is to be decreased, the resistance setting of variable resistor isincreased and less induced current is allowed to flow through coil30;'thus, the rate at which magnetism rises in magnet body 12 isincreased resulting in a stronger more rapid magnetic attraction ofarmature 60. it can be seen therefore that the clutch response time andthe amount of resistance in the electromagnetic circuit are inverselyproportional, i.e., the

time it takes armature 60 to respond to excitation of coil 20 may beincreased or decreased depending on whether the resistance in thecircuit is decreased or increased respectively.

When the electrical energy supplied to coil 20 is withdrawn, the fallingflux again generates a large momentary current in coil 30, this timeflowing in the opposite direction, (i.e., in the same direction as thecoil current) producing a magnetomotive force which aids the main fluxfield and therefore delays its collapse. Thus, armature 60 is moregradually released from its contact with the magnet body 12. The rate atwhich armature 60 is released from its contact with magnet body 12 canbe increased or decreased by increasing or decreasing the resistancesetting of variable resistor 100, response rate being the inverse ofresponse time. Switch Position C When clutch engagement is desired, acontrol signal is generated from the control circuit 50, coil 20 isenergized, and a voltage is induced across coil 30 as described above.Assuming the polarity of the primary coil 20 is such that the voltageinduced in coil 30 is in a clockwise direction, lead 93 will be ofpositive polarity and a circuit will be complete through slip ring 94,brush 95, external lead 96, diode 98, switch 91, variable resistor 100,through ground to coil lead 92. Since the diode 98 represents a very lowresistance path in its forward-conducting direction, a relatively largeeddy current will flow through coil 39 and the above external circuitduring flux build-up. The magnetomotive force created by this eddycurrent opposes that of the main coil current and results in slowing therate at which magnetism rises in magnet body 12. The flux of the mainmagnetic field, having to overcome this increased opposition, will buildmore slowly thereby retarding the movement of armature 60 intoengagement with magnet body 12; thus, clutch torque will be applied moregradually. Upon deenergization of primary coil 20, the voltage inducedin time delay coil 30 will be opposite in polarity from that inducedwhen coil 20 was energized.

Since diode )8 is substantially conductive in one direction only (fromanode to cathode) the eddy current path is now effectively blocked.Thus, no magnetomotive force is generated by coil 30 and armature 60will respond to the deenergization of coil 20 in a normal manner. Solong as the switch is in position C, the clutch will be slow toengage,but will disengage normally for every clutch engagement anddisengagement cycle. Of course, if the response rate of armature 60 isto be increased or decreased whenever primary coil 20 is energized, theresistance in the external control means 90 is also increased ordecreased respectively, by making the proper change in setting of thevariable resistor 100.

Switch Position D When clutch engagement is desired, a control signal isgenerated from the control circuit 50, coil 20 is energized, and avoltage is induced across coil 30 as described above. Again, assumingthat the primary coil polarity is such that the voltage induced in coil30 is in a clockwise direction, lead 93 will be of positive polarity anda circuit will be completed through slip ring 94, brush 95, externallead 96, diode 99, switch 91, variable resistor 100, through ground tocoil lead 92. However, since diode 99 is substantially conductive in onedirection only, the eddy current path is effectively blocked. Thus, nomagnetomotive force is generated by coil 30 and armature 60 will respondto the energization of coil 20 in a normal manner. Upon deenergizationof primary coil 20, the voltage induced in time delay coil 30 will beopposite in polarity from that induced when the coil was energized.Since diode 99 represents a very low resistance path in itsforwardconducting direction, a relatively large eddy current isconducted through coil 30 and the above external control circuit. Themagnetomotive force created by this current reinforces that of the maincoil current and results in slowing the rate at which magnetism decaysin the magnet body 12. The flux of the main magnetic field, being aidedby this additional magnetomotive force, will decay more slowly therebyretarding the movement of armature 60 away from engagement with magnetbody 12; thus, clutch torque will be released more gradually. Solong asthe switch is in position D, the clutch will have a normal engagementand a retarded disengagement every time coil 20 is energized anddeenergized. The rate at which armature 60 is released from its contactwith magnet body 12 can be increased or decreased by increasing ordecreasing the resistance setting of variable resistor 100.

One skilled in the art would be quick to recognize that the switchposition of switch 91 and the resistance setting of variable resistor190 could be controlled by either manual and/or automatic means the typeof control means used being a matter of design choice or being dictatedby the parameters of the overall clutch environment.

While only one preferred embodiment of this invention has beendisclosed, it will be apparent to those skilled in the art that changesmay be made to the invention as set forth in the appended claims, and,in some cases, certain features of the invention may be used toadvantage without corresponding use of other features. Accordingly, itis intended that the illustrative and descriptive materials herein beused to illustrate the principles of the invention and not to limit thescope thereof.

I claim:

1. In combination with an electromagnetic friction device of the typehaving a plurality of torque transmitting members, a magnet bodyoperatively associated with at least one of said torque transmittingmembers, an armature operatively associated with at least one other ofsaid torque transmitting members, said armature adapted to move towardand away from said magnet body, first electromagnetic coil means havingan electrical power lead operative to generate magnetic flux attractingsaid armature into clutch engagement when energized and operative torelease said armature from engagement when deenergized, and second coilmeans being in electromagnetic flux circuit relationship with said firstelectromagnetic coil means such that said first coil means causesanveddy current to be induced in said second coil means wheneverenergized and whenever deenergized, which eddy currents generatemagnetomotive opposition to change in flux levels thereby retarding themagnetic response of the armature both upon engagement anddisengagement, wherein the improvement comprises: j

adjusting means for selectively varying the amount of eddy currentpermitted to flow in the second coil means, said adjusting means beingin circuit relationship with the second coil means.

2. The combination as claimed in claim 1 wherein said adjusting meanscomprises variable resistance means connected in series circuitrelationship with the second coil means.

3. The combination as claimed in claim 1 including further switchingmeans in series circuit relationship with the second coil means and theadjusting means, said switching means having an open circuit position,and a closed circuit position.

d. The combination as claimed in claim 1. including further means forestablishing substantially unidirectional eddy current flow in thesecond coil means, said means being in circuit relationship with thesecond coil means and the adjusting means.

5. The combination as claimed in claim 4 wherein said means forestablishing substantially unidirectional eddy current flow in thesecond coil means comprises diode means connected in series circuitrelationship with the second coil means and the adjusting means.

6. The combination as claimed in claim 4 including further switchingmeans connected in series circuit relationship with the means forestablishing substantially unidirectional eddy current flow having anopen circuit position.

7. The combination as claimed in claim a including further switchingmeans connected in parallel circuit relationship with the means forestablishing substantially unidirectional eddy current flow having aclosed circuit position which bypasses the means for establishingsubstantially unidirectional eddy current flow.

8. The combination as claimed in claim 4 including further switchingmeans connected in series circuit relationship with the means forestablishing substantially unidirectional eddy current flow having aposition for selectively varying the amount of eddy current flow in thesecond coil means when the first coil means is energized.

1. In combination with an electromagnetic friction device of the typehaving a plurality of torque transmitting members, a magnet bodyoperatively associated with at least one of said torque transmittingmembers, an armature operatively associated with at least one other ofsaid torque transmitting members, said armature adapted to move towardand away from said magnet body, first electromagnetic coil means havingan electrical power lead operative to generate magnetic flux attractingsaid armature into clutch engagement when energized and operative torelease said armature from engagement when deenergized, and second coilmeans being in electromagnetic flux circuit relationship with said firstelectromagnetic coil means such that said first coil means causes aneddy current to be induced in said second coil means whenever energizedand whenever deenergized, which eddy currents generate magnetomotiveopposition to change in flux levels thereby retarding the magneticresponse of the armature both upon engagement and disengagement, whereinthe improvement comprises: adjusting means for selectively varying theamount of eddy current permitted to flow in the second coil means, saidadjusting means being in circuit relationship with the second coilmeans.
 2. The combination as claimed in claim 1 wherein said adjustingmeans comprises variable resistance means connected in series circuitrelationship with the second coil means.
 3. The combination as claimedin claim 1 including further switching means in series circuitrelationship with the second coil means and the adjusting means, saidswitching means having an open circuit position, and a closed circuitposition.
 4. The combination as claimed in claim 1 including furthermeans for establishing substantially unidirectional eddy current flow inthe second coil means, said means being in circuit relationship with thesecond coil means and the adjusting means.
 5. The combination as claimedin claim 4 wherein said means for establishing substantiallyunidirectional eddy current flow in the second coil means comprisesdiode means connected in series circuit relationship with the secondcoil means and the adjusting means.
 6. The combination as claimed inclaim 4 including further switching means connected in series circuitrelationship with the means for establishing substantiallyunidirectional eddy current flow having an open circuit position.
 7. Thecombination as claimed in claim 4 including further switching meansconnected in parallel circuit relationship with the means forestablishing substantially unidirectional eddy current flow having aclosed circuit position which bypasses the means for establishingsubstantially unidirectional eddy current flow.
 8. The combination asclaimed in claim 4 including further switching means connected in seriescircuit relationship with the means for establishing substantiallyunidirectional eddy current flow having a position for selectivelyvarying the amount of eddy current flow in the second coil means whenthe first coil means is energized.
 9. The combination as claimed inclaim 4 including further switching means connected in series circuitrelationship with the means for establishing substantiallyunidirectional eddy current flow having a position for selectivelyvarying the amount of eddy current flow in the second coil means whenthe first coil means is deenergized.